A couple of reports surfaced this month about a station in Louisiana changing frequencies due to interference to aviation radio channels. The 50,000-watt station in question broadcast on 107.9 FM and is owned by Cumulus Broadcasting, and the interference reportedly involved intermodulation between it and another station in east Texas.
Unlike last year’s hype of a pirate station in Florida interfering with aircraft communications, the Louisiana interference affected the instrument navigation signals of several airports, including the Barksdale Air Force Base.
This is an important point: aviators usually have several radio channels available to talk with ground controllers and other aircraft, but there’s not that same sort of redundancy for radio navigation systems. And whereas in Florida a guy in a helicopter reported the problems (meaning he could precisely control the location of his aircraft in order to pick out the worst areas of interference to hype), this was affecting all aviation in the area.
Although the FCC, FAA, and Air Force have been looking into the problem “for weeks,” the offending station has since moved down the dial, displacing another Cumulus-owned station until the situation is resolved (it certainly didn’t help Cumulus that the interference-generating station happened to be the top-rated station in the local cluster).
The general manager of the Cumulus cluster in Shreveport, C.J. Jones, explains the situation this way:
It’s a whole bunch of weird, should-never-happen circumstances that came together and nobody foresaw it. We never had any reports of aircraft that ever went off the flight path or got in any danger, but I can understand the concern, being in these monstrous aircraft and you’re going along and all of a sudden you’ve got a great song in your ear.
The real problem here is one the National Association of Broadcasters tried to pin on LPFM back in the day: the “shoehorning” of stations into places on the FM dial where they probably don’t belong. If offending stations in question operated at lower power levels and/or were required to have more distance separation between them this problem never would have occurred. Commercial broadcasters, however, have whittled away at interference protection rules over the years to the point where problems like this do occur – and they are undoubtedly more commonplace than what gets reported.
While researching this story I found this interesting document which reports problems of radio interference on C-130 cargo/combat aircraft. It appears that RF from the planes’ own radio communication devices can bleed into the electronics that provide engine propeller control on the aircraft, leading to an unannounced loss of power. This just goes to show that interference to aircraft doesn’t even have to involve an external source.
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